MotoMatters.com | Kropotkin Thinks

The upper exhaust on the KTM RC16, for the rear cylinder bank of the V4. No torque back pressure valve on it, unlike the Ducati and Aprilia.
The mesh on the end of the exhausts was introduced when the number of engines per season were limited after the 2008 financial crisis. The mesh prevents sizable stones from entering the engine and damaging it in the case of a crash.

Suzuki's Akrapovic-made 4-into-1-into-2 exhaust is exqusite in every way. Note the pipe joining the two exhausts just before the end. Stabilizes them. What's remarkable is that the exhaust is unchanged for this year, despite the engine producing a lot more power.

The Yamaha M1 uses another Akrapovic-made pipe (Akrapovic suppliers four of the six MotoGP factories). This particular pipe is so clean it is unused. You can see the weld on the interior part of the pipe, through the honeycomb mesh.

Both Aprilia pipes, newly fitted again, as you can see by how clean the inside of the lower pipe is. Like the Ducati and Honda, the exhaust pipes consist of two 2-into-1 pipes, one for each bank of cylinders of the V4. But upper and lower pipes are slash-cut to give them a larger surface area.
Aprilia switched from Akrapovic to SC Project this year, and the exhausts have undergone a slight redesign

Here's the upper exhaust, from the rear cylinder bank. Torque back pressure valve is on top, which opens and closes to produce more back pressure at low revs.
This exhaust is slash-cut now, unlike the early part of last year. This gives the exhaust a larger exit surface without increasing the diameter of the pipe.

The lower pipe. It is a slightly different shape, a little stubbier than last year's example. It may also be slightly larger, if the scratches on the surface are anything to go by. It is clearly touching down in corners.
The soot on the beehive mesh is another sign this pipe has been used in anger.

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